GNU Collaborative International Dictionary of English

Found one definition

  1.       
    
    lepton n. (Physics) an elementary particle that participates in weak interactions but does not participate in the strong interaction; it has a baryon number of 0. Some known leptons are the electron, the negative muon, the tau-minus particle, and the neutrinos associated with each of these particles.
    WordNet 1.5
    +PJC